1. Field of the Invention
The present invention relates to switching equipment for setting up a telephone connection between at least two telephone subscribers which can be employed both in a public exchange, wherein inter-exchange lines for connection to the public telephone network are connected in addition to local subscribers, and in a private telephone private branch exchange.
2. Description of the Prior Art
As known, such switching equipment is utilized for setting up a telephone connection between two pieces of telephone terminal equipment or, respectively, between terminal equipment and an exchange line connected to the switching equipment. The switching equipment, thereby, particularly serves to select and to switch the corresponding connecting path. As a result of a connection setup, voice information or data are exchanged or, respectively, transmitted between the corresponding subscribers via the switching equipment. The transmission of this voice information is, thereby, usually subject to a charge; i.e., the subscribers must pay fees to the operator of the switching equipment as well as to the operator of the telephone network connected thereto for the duration of the setup and maintenance of the connection. These charges are generally born by the calling party.
In addition to the actual connection setup for the purpose of a transmission of voice information, modern exchanges offer further services that can be used by the subscribers connected thereto subject to a charge. One of these additional services, for example, is being informed of the telephone number of the calling party. In this way, the called party or, respectively, the recipient is informed of the telephone number of the calling party during the setup of the telephone connection wherein, for example, such number is displayed on a display of his telephone set. The called party [sic] can, thus, identify the calling party before accepting the call. It is known to connect an incoming call through to a busy subscriber who is already speaking to another subscriber. This procedure is generally referred to as xe2x80x9ccall waiting,xe2x80x9d wherein the called party is informed of the arrival of a new call by, for example, an acoustic signal with which the telephone number of the calling party can be output. The called party can, thus, decide whether he wishes to end the existing connection and accept the newly arriving call. It is likewise possible to switch between the two connections. Given digital telephone networks such as, for example, the ISDN, these services already have been largely realized.
For making use of such a service, as a result whereof further information is transmitted via the switching equipment or, respectively, this connecting path in addition to the voice information, a lump-sum, for example a basic monthly fee, is usually charged. Such change is typically independent of the duration of the connection setup.
Such switching equipment includes a central or coordination processor that controls the transmission of the voice and auxiliary information between two subscribers or, respectively, between a subscriber and a public exchange line. Further, the switching equipment includes a plurality of exchange units to which a plurality of subscribers (i.e., terminal equipment) or, respectively, a plurality of the inter-exchange lines are respectively connected. Each of these exchange units thus serves for the administration of that information which refers to the subscribers respectively connected thereto. The exchange units include separate transmission units for the voice and auxiliary information. Whereas the central processor coordinates the individual exchange units, each exchange unit has an exchange processor means (referred to below simply as exchange processor) that is provided for the control of the corresponding exchange unit and, in particular, coordinates the transmission of the voice or, respectively, additional information within an exchange unit.
For example, the transmission of the telephone number of the calling party thereby occurs as follows: an arriving call is communicated to the central processor via the corresponding exchange assembly or, respectively, exchange unit to which the calling party also is connected, whereby the telephone number of the calling party is communicated to the central processor. On the basis of the destination telephone number selected by the calling party, the central processor identifies the corresponding, called subscriber and selects that exchange unit that is responsible for the called subscriber. The exchange processor present in the exchange unit accesses a list in which a note as to whether the individual subscriber is technologically ready for the reception and the display of telephone numbers, and is also authorized to do so (for example, by paying a monthly lump-sum fee), is entered for every subscriber connected to this exchange unit. In this way, the exchange unit checks whether the telephone number of the calling party can be transmitted to the called subscriber. The result of this check is communicated from the exchange processor of the transmission unit to the central processor. As a rule, each exchange unit may include one or more transmission units for the transmission of telephone numbers. When the result of the check by the exchange unit in view of the reception authorization of the telephone number of a calling party was positive, the central processor selects one of the transmission units and informs this transmission unit of the telephone number of the calling party so that the selected transmission unit can send the telephone number to the requested subscriber.
Since the exchange processor provided in each exchange unit also serves for the control or, respectively, coordination of the transmission of voice information via the corresponding exchange unit, it can be seen that an additional load on the exchange processor of the corresponding exchange unit is produced by offering the possibility of transmitting further auxiliary information such as, for example, the telephone number of a calling party, in addition to the voice information. Since each exchange processor serves for the setup or, respectively, cleardown of the individual connections, the load on the exchange processor increases given shorter connection durations. In particular, the duration of the occupancy of a transmission unit within an exchange unit provided for the transmission of the telephone number is relatively short and amounts, for example, to less than three seconds, so that the corresponding transmission unit, after receiving the request for transmission of the telephone number, converts this request into a corresponding signal to the desired subscriber within three seconds. Due to this short occupancy duration of the transmission units provided for the transmission of the telephone numbers, an intense usage of this performance feature can arise, so that an overload of the exchange processor can occur. An overload of the exchange processor, however, is at the expense of the actual switching technology, i.e. of the connection setup for voice information, since an exchange unit, given an overload of the corresponding exchange processor, must react with self-limitation, i.e. rejects new occupancy requests, so that the actual switching technology, i.e. the connection serving for the actual transmission of voice information, can be displaced due to an intense utilization of the possibility of telephone number transmission. Since, given an overload, the corresponding exchange unit rejects a certain percentage (for example, between 25 and 100%) of the newly arriving occupancy requests dependent on the degree of overload, these calls are lost. Operators thus also lose the charges that would otherwise have arisen given these calls.
The present invention is therefore based on the object of fashioning a switching equipment according to the preamble of claim 1 such that an intense utilization of the transmission possibility of additional information is not at the expense of the normal call processing, i.e. transmission of voice information.
This object is inventively achieved by a switching equipment according to claim 1.
The subclaims describe advantageous embodiments of the present invention.
Inventively, monitoring means are provided that monitor the degree of usage of the individual exchange processors and, after identifying an impending overload of an exchange processor, delay the enable of the transmission unit of an arbitrary exchange unit provided for the transmission of additional information; for example, telephone numbers.
In particular, the occupancy duration of the transmission unit provided for the transmission of additional information is artificially lengthened in this way dependent on the degree of usage of the corresponding exchange processor. The occupancy of the transmission unit of an exchange unit provided for the transmission of additional information is known to the central processor. Upon arrival of a request for telephone number transmission, the central processor selects a transmission unit initially identified as free and marks this as busy. After the end of the transmission of the telephone numbers, the corresponding exchange unit, in turn, reports the release of the transmission unit to the central processor. Since, in case of an overload of an exchange processor, the transmission unit provided for the transmission of additional information is reported to the central processor as busy longer than normally required, this transmission unit of the corresponding exchange unit cannot be employed for the transmission of telephone number information or other terminal equipment-related additional information. As such, no additional load on the exchange processor can occur in the corresponding exchange unit due to the transmission of such supplementary information by this transmission unit that is busy for a longer time. The exchange processor of the corresponding exchange unit can thus recover. An adequate capacity is always present for the xe2x80x9cnormalxe2x80x9d call processing; i.e., for the actual switching technology for the transmission of voice information.
The above-described defense measure is advantageously already activated before the actual load of the corresponding exchange processor becomes so high that newly arriving calls must be rejected. This means that the inventively provided monitoring means already can recognize an impending overload of the exchange processor before an overload of the exchange processor can actually occur. For this reason, a specific load limit value is defined, wherein the monitoring means responds when this is upwardly transgressed and artificially lengthens the occupancy time of the transmission unit provided for the transmission of supplementary information.
This load limit value lies below that usage degree that would, in fact, lead to an overload of the corresponding exchange processor.
In this way, a certain priority over the transmission of supplementary information such as, for example, the transmission of the telephone number of a calling party that is usually charged with a lump sum, is accorded to the actual, chargeable switching technology for the transmission of voice information.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawings.